Fuel igniters



J. G. COHN FUEL IGNITERS May 10, 1955 5 Sheets-Sheet 1 Filed Nov. 18,1950 INVEN TOR. fizz/ ief (5/522 ATTORNEY 10, 1955 J. G. COHN 2,708,252

FUEL IGNITERS Filed Nov. 18, 1950 5 Sheets-Sheet 2 WIRE: 2 Strands, each0.0027" Diameter PRIMARYWINDING: 44 T.P. I. on 0.010" Mandrel SECONDARYWINDING: on 0.040 Mandt'el 1 Sec.

1%. Sec

-12 2 Se c 1000 a: Q) v:

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5 700 21 18 16 14 Spacing of Secondary Winding (T. P. I.)

INVENTOR.

ATTORNEY y 0, 1955 J. G. COHN 2,708,252

FUEL IGNITEZRS WIRE: 2 Strands, each 0.0027"Diameter PRIMARY WINDING: 32T.P.I. on 0.010" Mandrel SECONDARY WINDING: 0110.070 Mandrel Filed Nov.18, 1950 5 Sheets-Sheet 5 /1 Sec.

A 2 a 2 Sec. 1000 5 31 '18 16 14 12. 5 Spacing of Secondary Winding (T.P. I.)

INVENTOR.

Ma Gazzf/SWCZ/Frz ATTORNEY y 1955 J. G. COHN 2,708,252

FUEL IGNITERS Filed Nov. 18, 1950 5 Sheets-Sheet 4 WIRE= 2 Strands each0.0035"DiameTer PRIMARY WINDING: 441121. on 0.010" Mandrel SECONDARYwmnmq: on 0.070"Mandre1 Ignition Spee 1 (Sec. X 10) 0 L 21 18 16 14 12-5 Spacing of Secondary Winding (T.P.I.)

INVENTOR. Ila/fax: Gzmlzer (fa/F2:

ATTORNEY J. G. COHN FUEL IGNITERS May 10, 1955 5 Sheets-Sheet 5 FiledNov. 18, 1950 WIRE 2 strandsfeack 0.0055"Diamder PRIMARY WINDING: 22T.P. 1. cm 0.010"Mandre1 SECONDARY wmnmq: on 0.070" Mandrel c e S 1.

700 14 12.5 Spacing of Secondary Winding (T.P.I.)

p. A J 4 n u I m3 uw mv 6 m 333 a I N V EN TOR. Join 6222f)? 62%? IATTORNEY FUEL IGNETERS Eohan Gunther Cohn, East Grange, N. 3., assiguorto Baker & Co, Inc., Newark, N. J., a corporation of New JerseyApplication November 18, 1950, Serial No. 196,421

6 Claims. (Cl. 317--33) This invention deals with automatic ignition ofgasair mixtures by the combined effect of electrically and catalyticallyproduced heat and more particularly with igniter elements which, wheninserted into an electric circuit which preheats them, are able, owingto additional catalytically produced heat, to ignite a flow ofdiflicultly ignitable organic fuehair mixtures contacting them. Suchigniter elements consist of wire structures mounted on a carrier withcontacts for easy connection to an electric circuit. The wire structuresheretofore known had the form of a helical wire coil usually so closelyspaced that contact between its windings was barely avoided, the coilconsisting of catalyst wire of a diameter in the range of about 0.001inch to about 0.003 inch. The coil can be formed in such a way that anon-uniform structure is attained, i. e. in at least one portion of thecoil the wires are closer together than in the remainder of the coil, inorder that at least one por tion is heated up quickly by catalyticaction in fiameless combustion, and flame ignition occurs on theremainder according to the heterophase principle. The most suitablestructural form is the coiled coil. It had been thought that therestrictions on the wire diameter set forth above, which have been usedfor the plain coil, can also be applied to heterophase structures.

When an igniter coil is subjected to even a low degree of electricpreheating this does not exclude short moments during each ignitioncycle in which the coil is subjected to a thermal shock of peaktemperature (which in the case of methane may be as high as 1600" C. tol700 C.). The thin wires used previously might not be able to stand suchshocks. However, making the structure from a thicker wire would notnecessarily help, since greater wire diameter results in lowertemperature increase due to greater heat capacity and greater heat lossby conduction and, in general, reduces the efiiciency of the igniter.

it has now been found that the increase in catalytic efficiency broughtabout by the heterophase wire structure can be made so effective thatunder certain conditions it can outweigh any diminution in elficiencywhich the use of the thicker wire involves. This may be utilized insingle wire structures, but it becomes more effective and of greaterimport it stranded wire is used for the construction of the coil. inorder to apply the hetcrophase principle in a coiled-coil stranded-wi econstruction many factors concerning the geometrical configuration mustbe considered in order to obtain optimum efficiency in operation. Thevarious factors which influence ignition speed include the diameter ofthe wire, the inner diameter or mandrel of the primary coil, the spacingof the primary coil, the mandrel of the secondary coil, and the spacingtates Patent ice of the secondary coil. It is therefore an object ofthis invention to so construct an igniter coil considering the variousfactors just enumerated as to obtain speedy and eflicient ignition. Itis a further object of the invention to so construct a stranded wire asto be operable in a catalytic igniter combination to obtain speedyignition with optimum etiiciency.

Other objects and advantages of the invention will be more fullydescribed hereinafter, reference being had to the accompanying drawings,in which:

Figure l is a diagram of a conventional automatic ignition system.

Figure 2 is a schematic View of the igniter element of the ignitionsystem having a coiled coil structure.

Figure 3 is an elevational view or" a few windings of a primary coil.

Figures 4 to 7 represent space diagrams illustrating the variousgeometrical considerations of wire structure mentioned hereinabove, inwhich, ignition speed is plotted in relation to various factors.

In Figure 1 there is shown the burner i, which has in addition to thegas outlets in its upper portion, a flash port 2, a flash tube 3 leadingto a housing 4 (which is only schematically indicated). The igniterelement 5 is connected by leads 6 and 6 to an electric power source 7.

As shown in Figure 2 the ignitcr element 5 is a coiled coil supported byleads 6 and 6, and is mounted on a plug 8, which has contacts 9 and 9for connection to an electric circuit.

Figure 3 depicts the specific geometrical relationships of a coiled coilstructure, wherein the inner diameter of the primary coil is shown at1%, the spacing of the secondary coils is shown at 11, and the mandrelor the inner diameter of the secondary coil is shown at 12.

The space diagrams 4 to 7 relate various relationships of wireconstruction to ignition speed. For purposes of this application theignition speed is defined as the reciprocal of the ignition time inseconds, multiplied by ten. The ignition speed is plotted as a functionof coil temperature in C., and or" the spacing of the windings of thesecondary coil in turns per inch (T. P. L). The various constants areindicated at the top of the graphs. The graphs also contain theisochrones for ignition within 1, 1.25 and 2 seconds, i. e. the planesin the space diagrams containing all combinations of temperature andsecondary spacing at which ignition occurs within the time intervalsstated. In order to show how a change in the factors marked on the topof the graphs influences the three variables shown in the space diagramof Figure 4, the results with other wire diameters and/ or other valuesof mandrels of primary and secondary coils are shown in Figures 5-7. Theresults shown in Figures 4-7 are intended to illustrate the criticalityof the various geometrical relationships of coil structure that I havedetermined.

A standard test apparatus was used for all tests. In order to make thetime differences under varying conditions more precisely determinable,the ignition time required was unusually lengthened, thus making alltests take place under conditions of operation more severe than thoseencountered in actual usage. The test gas used throughout was straightmethane, the gas pressure and the addition of air chosen were also moreunfavorable than usually cncountered in the average usage and the flashtube was so adjusted as to retard ignition. The ignition time consistsof the period from the opening of the gas valve including ignition ofthe gas-air mixture on the catalyst, and flashing back of the flamethrough the flash tube up to the time the main burner is ignited.Obviously, the most suitable igniter will be one which needs the lowesttemperature to execute ignition within a given time. Another aspect tobe considered is that the igniter should obtain favorable operatingcharacteristics even though there be slight dimensional variations inthe spacing of the secondary coil, since such variations cannot beavoided in mass production.

All tests were made with coiled coil structures using the heterophaseprinciple and stranded wire was used for the formation of the primarycoil. As used hereinafter, the term efiective wire diameter is definedas the diameter of the wire in a single strand igniter coil and alsoincludes within its scope that diameter of a single strand wire which incross-section has the same area as the sum of the cross-sectional areasof each wire strand of a stranded wire igniter coil.

In Figures 4 and 5, the coil consisted of two wire strands, each ofwhich had a diameter of 0.0027", the two wire cross-sections togetherbeing equal to the crosssection of a single wire of 0.00382 diameter;(i. e. the effective wire diameter is 0.00382); the primary coil had amandrel of 0.010". The spacing of the primary coil was 44 T. P. I.(turns per inch) in Figure 4, and 32 in Figure 5. The mandrel of thesecondary coil was 0.040 in Figure 4 and 0.0070" in Figure 5.

In Figures 6 and 7, the coil used consisted of two wire strands, each ofwhich had a diameter of 0.0035, the two wire cross-sections togetherbeing equal to the crosssection of a single wire of (or having aneffective wire diameter of) 0.00495". The mandrel used for the primarycoil in the tests of Figures 6 and 7 was 0.010", which is the same asthat used in the tests of Figures 4 and 5. The mandrel of the secondarycoil used in the tests of Figures 6 and 7 was 0.070, which is the sameas that used in Figure 5; and the spacing of the primary coil was 44 T.P. I. in Figure 6 and 22 T. P. I. in Figure 7.

Figures 4 to 7 show how with a change of spacing of the secondary coil,the degree of preheating temperature necessary to bring about ignitionwithin a certain time changes. The curves of the diagrams were based onthe following values of the variables:

Figure 4 Secondary Coil Spacing (Turns Per Inch) Figure 5 Secondary CoilSpacing Temperature Ignition Time Igmition (Turns Per Inch) in C.

in Seconds Speed Figure 6 Secondary Coil Spacing in Seconds IgnitionSpeed Figure 7 Ignition Speed Secondary Coil Spacing TemperatureIgnition 'lime (Turns Pei Inch) m C. in Seconds In comparing the resultsshown in Figure 4 with those of Figure 5 it is seen that for the sameignition speeds the geometrical construction used in the tests of Figure5 obtains lower coil temperatures. Thus, for an ignition time of onesecond, where the spacing of the primary coil is 44 T. F. I., and themandrel of the secondary coil is 0.040 (see Fig. 4), the temperaturerequired for a spacing of the secondary winding of 14 T. P. I. was 950C., whereas with a spacing of the primary coil of 32 T. P. I. and amandrel of 0.070 for the secondary coil (Figure 5), the correspondingtemperature was found to be only 810 C. Thus, the preheating temperaturewas brought down by as much as 140 C., by a wider spacing of the primarycoil of from 44 to 32 T. P. I., and by increasing the mandrel of thesecondary coil from 0.040" to 0.070". These tests show how critical evenslight variations in the dimensions of the coiled-coil structure are. Asstated previously, the temperature range used in the tests is ratherhigh (700 C. to 1050 C.).

In the tests of Figures 6 and 7, both carried out with stranded wires,each strand being of 0.0035" diameter, the effect of changing thespacing in the primary coil, from 44 T. P. I. (Figure 6) to 22 T. P. I.(Figure 7) was examined. The preheating temperature necessary forignition within one second for a spacing of the secondary winding of 18T. P. I. was found to be 1015 C. in Figure 6; and 900 C. in Figure 7.Thus the structure used in the tests of Figure 7 resulted in a loweringof the preheating temperature for similar conditions of as much as 115C. Similar conclusions are to be drawn when examining the temperaturesneeded for ignition within 1% and 2 seconds.

From an analysis of these various tests I have found that, althoughworking with thicker wires increases the difiiculties of ignition (aboveabout 0.003" effective wire diameter) it is possible to obtain quickignition by wider spacing of the primary coil, and a wider mandrel ofboth coils.

If the Figures 4 and 5 are compared with Figures 6 and 7 and especiallyif Figures 5 and 7 are compared, it is readily seen that with increasingwire diameter the ignition difiiculties increase; but it is also evidentthat by choosing the other dimensions within the ranges indicated, it ispossible even with an effective wire diameter of up to about 0.005 andabove to remain below the ignition point of methane. Because of thehigher resistance of sturdier structures to thermal shocks, this is avery accountable advantage in practice. At the same time, the tests showalso, that with an effective wire diameter of about 0.006, it ispossible to come fairly close to the permissible upper limit of the wirediameter, if the other dimensions are adjusted to the most favorableconditions revealed above.

From all the tests 1 have made I find that, to obtain the most efiicientignition operation, it is preferred that the primary mandrel should beabout 0.010 and the secondary mandrel should have a diameter of about0.070". For coils made of 2 strands of wire with 0.0027

diameter each, the preferred spacing of the primary winding should be 32T. P. I. and the preferred spacing of the secondary winding should bewithin the range of 8 to 18 T. P. I. For coils made of two strands of0.0035" wire each the optimum structure was about the same, except thatthe spacing of the primary winding should preferably be 22 T. P. I.

The results obtained from the tests are surprising, since ordinarilyquick ignition theoretically requires close heat concentration in asmall space and it would be expected that a closer and not a widerspacing of coils should be used. Also, since a thicker wire means agreater heat loss, it would have been expected that, when increasing thewire size, the mandrel and spacing should be dimensioned so that thewindings are as close together as possible in order to increase heatconcentration. But I found that the mandrel and spacing of the coiledcoil must be so chosen that the windings are relatively farther apartfrom each other, in order to reach quick ignition. I believe that theexplanation for this is that spacing the windings somewhat farther apartin a heterophase structure permits convection currents to dilute theatmosphere between the turns, and thereby decrease detrimentalblanketing and facilitate ignition. The unexpected excellent resultsachieved with thicker stranded wires indicate that, although the totalcross-section of such wire of the tests as indicated in Figures 6 and 7is equivalent to the cross-section of a single unstranded wire of 0.005"diameter (and, accordingly, the electric resistance is the same in bothcases) the catalytic action and surface combustion is greater in thecase of stranded wire. Two Wires stranded together act catalytically tosome extent as if they were suspended in parallel to each other withonly partial contact between them.

Whereas the dimensional restrictions set forth hereinabove are notessential to igniter coil structures made of thinner wire, thesedimensions have been found to be critical in coiled coil structures madeof thicker wire in the range of about 0.003" to 0.006" effective wirediameter. While in the lower part of this latter range they markedlyimprove the efiiciency, it is only by using such dimensionalrestrictions that ignition can be obtained at low temperatures in theupper part of the range.

The igniter element of this invention quickly and safely ignitesdifiicultly ignitable fuel-air mixtures on heating below their ignitionpoint and below the recrystallization temperature of the catalystmaterial.

he preferred catalyst matall is metal of the platinum group, especiallyplatinum itself or its alloys, e. g. alloys with iridium or rhodium.

Although my invention has been described in some detail hereinabove, itis susceptible of modification and 1 do not intend that it be limitedother than by the scope of the appended claims.

What 1 claim is:

1. An automatic igniter element for organic fuels in finely dividedstate capable of being catalytically oxidized in a fuel-air mixture inthe presence of a catalyst, comprising a coiled wire structure having acatalytically active material thereon, said element being provided withmeans for connection to a source of electrical power to heat said coilstructure to a temperature substantially below the ignition temperatureof said fuel in said fuelair mixture, the wire structure of said coilhaving an effective diameter exceeding at least about 0.003, said coiledstructure consisting of a series of primary coils being in turn formedinto a secondary coil having a plurality of turns, said primary coilshaving a coil spacing of from about 10 to about 35 turns per inch.

2. The element of claim 1 wherein said secondary coils have a spacing offrom about 8 to about 18 turns per inch.

3. An automatic igniter element for organic fuels in finely dividedstate capable of being catalytically oxidized in a flowing fuel-airmixture in the presence of a catalyst, said element being provided withlead-in wires for connection with a source of electrical power,comprising a coiled wire structure having a catalytically activematerial at least on its surface, the wire coiled structure having aneffective diameter of between about 0.003 and about 0.006", said coiledstructure consisting of a series of primary coils being in turn formedinto a secondary coil having a plurality of turns, said primary coilshaving a coil spacing of about 10 to about 35 turns per inch.

4. The igniter element of claim 3 wherein said secondary coils have aspacing of from about 8 to about 18 turns per inch.

5. An igniter element according to claim 1 in which the coils are formedof a two stranded wire, each strand of which has a diameter of 0.0027and the primary coils have a spacing of about 32 turns per inch.

6. An igniter element as defined in claim 1 in which the coils areformed of a two-stranded wire, each strand of which has a diameter of0.0035 and the primary coils have a spacing of about 22 turns per inch.

References (Jitetl in the file of this patent UNITED STATES PATENTS567,928 Van Hoevenbergh Sept. 15, 1896 614,583 Simonini Nov. 22, 18981,118,942 Lyon Dec. 1, 1914 1,994,390 Gibson Mar. 12, 1935 2,406,172Smithells Aug. 20, 1946 2,487,752 Cohn Nov. 8, 1949 2,487,753 Cohn Nov.8, 1949 2,487,754 Cohn Nov. 8, 1949 2,530,827 Lakato Nov. 21, 1950

